We present visible multi-band photometry of trans-Neptunian objects (TNOs) observed
by the Subaru Telescope in the framework of the Hyper Suprime-Cam Subaru Strategic
Program (HSC-SSP) from 2014 March to 2016 September. We measured the five broad-band
(g, r, i, z, and Y) colors over the wavelength range from 0.4 μm to 1.0 μm for 30
known TNOs using the HSC-SSP survey data covering ∼ 500 deg2 of sky within ±30°
of ecliptic latitude. This dataset allows us to investigate the correlations between the
dynamical classes and visible reflectance spectra of TNOs. Our results show that the
hot classical and scattered populations with orbital inclination (I) of I >~ 6° share similar
color distributions, while the cold classical population with I <~ 6° has a different color
distribution from the others. The low-I population has reflectance increasing toward
longer wavelengths up to ∼ 0.8 μm, with a steeper slope than the high-I population at
<~ 0.6 μm. We also find a significant anti-correlation between g−r/r−i colors and
inclination in the high-I population, as well as a possible bimodality in the g−i color vs.
eccentricity plot.

Published in:
Publications of the Astronomical Society of Japan, 70, S40

Reflection spectroscopy in the Near Infrared (NIR) is used to
investigate the surface composition of Trans-Neptunian objects (TNOs).
In general, these spectra are difficult to interpret due to the low
apparent brightness of the TNOs, causing low signal-to-noise ratio even
in spectra obtained with the largest telescopes available on the Earth,
making necessary to use filtering techniques to analyze and interpret
them.

The purpose of this poster is to present a methodology to analyze the
spectra of TNOs. Specifically, we aim at filtering these spectra in the
best possible way: maximizing the remotion of noise, while minimizing
the loss of signal. To do this, we use the wavelets technique. The
wavelets are a mathematical tool that decomposes the signal into its
constituent parts, allowing to analyze the data in different areas of
frequencies with the resolution of each component tied to its scale. To
check the reliability of our method, we compare the filtered spectra
with spectra of water and methanol ices to identify some common
structures between them.

Of the 50 TNOs of our sample, we identify traces of the presence of
water ices and methanol in the spectra of several of them, some with
previous reports, while some of these objects there were no previous
reports. Therefore, we conclude that the wavelet technique is successful
in filtering TNOs spectra.

The Trojan asteroids of Jupiter and Neptune are likely to have been
captured from original heliocentric orbits in the dynamically excited
("hot") population of the Kuiper belt. However, it has long been
known that the optical color distributions of the Jovian Trojans and the
hot population are not alike. This difference has been reconciled with
the capture hypothesis by assuming that the Trojans were resurfaced (for
example, by sublimation of near-surface volatiles) upon inward migration
from the Kuiper belt (where blackbody temperatures are ∼ 40 K) to
Jupiter's orbit ( ∼ 125 K). Here, we examine the optical color
distribution of the Neptunian Trojans using a combination of
new optical photometry and published data. We find a color
distribution that is statistically indistinguishable from that of the
Jovian Trojans but unlike any sub-population in the Kuiper belt. This
result is puzzling, because the Neptunian Trojans are very cold
(blackbody temperature ∼ 50 K) and a thermal process acting to
modify the surface colors at Neptune's distance would also affect the
Kuiper belt objects beyond, where the temperatures are nearly identical.
The distinctive color distributions of the Jovian and Neptunian
Trojans thus present us with a conundrum: they are very similar to each
other, suggesting either capture from a common source or surface
modification by a common process. However, the color distributions
differ from any plausible common source population, and there is no
known modifying process that could operate equally at both Jupiter and
Neptune.

The data returned from NASA's New Horizons reconnaissance of the Pluto
system show striking albedo variations from polar to equatorial
latitudes as well as sharp longitudinal boundaries. Pluto has a high
obliquity (currently 119°) that varies by 23° over a
period of less than 3 million years. This variation, combined with its
regressing longitude of perihelion (360° over 3.7 million years),
creates epochs of "Super Seasons" where one pole is pointed at the Sun
at perihelion, thereby experiencing a short, relatively warm summer
followed by its longest possible period of winter darkness. In contrast,
the other pole experiences a much longer, less intense summer and a
short winter season. We use a simple volatile sublimation and deposition
model to explore the relationship between albedo variations, latitude,
and volatile sublimation and deposition for the current epoch as well as
historical epochs during which Pluto experienced these "Super Seasons."
Our investigation quantitatively shows that Pluto's geometry creates the
potential for runaway albedo and volatile variations, particularly in
the equatorial region, which can sustain stark longitudinal contrasts
like the ones we see between Tombaugh Regio and the informally named
Cthulhu Regio.

Pluto's surface is covered by volatile ices that are in equilibrium with
the atmosphere. Multicomponent phase equilibria may be calculated using
a thermodynamic equation of state and, without additional assumptions,
result in methane-rich and nitrogen-rich solid phases. The former is
formed at temperature range between the atmospheric pressure-dependent
sublimation and condensation points, while the latter is formed at
temperatures lower than the sublimation point. The results, calculated
for the observed 11 microbar atmospheric pressure and composition, are
consistent with recent work derived from observations by New Horizons.

To appear in:
Monthly Notices of the Royal Astronomical Society, 474, 4254

In light of the recent New Horizons flyby measurements, we
present a coupled ion-neutral-photochemistry model developed for
simulating the atmosphere of Pluto. Our model results closely match the
observed density profiles of CH4, N2 and the C2 hydrocarbons in
the altitude range where available New Horizons measurements are
most accurate (above ∼ 100-200 km). We found a high eddy
coefficient of 106 cm2 s−1 from the surface to an altitude of
150 km, and 3 ×106 cm2 s−1 above 150 km for Pluto's
atmosphere. Our results demonstrate that C2 hydrocarbons must stick
to and be removed by aerosol particles in order to reproduce the C2
profiles observed by New Horizons. Incorporation into aerosols in
Pluto's atmosphere is a significantly more effective process than
condensation, and we found that condensation alone cannot account for
the observed shape of the vertical profiles. We empirically determined
the sticking efficiency of C2 hydrocarbons to aerosol particles as a
function of altitude, and found that the sticking efficiency of C2
hydrocarbons is inversely related to the aerosol surface area. Aerosols
must harden and become less sticky as they age in Pluto's atmosphere.
Such hardening with ageing is both necessary and sufficient to explain
the vertical profiles of C2 hydrocarbons in Pluto's atmosphere. This
result is in agreement with the fundamental idea of aerosols hardening
as they age, as proposed for Titan's aerosols.

Published in:
Monthly Notices of the Royal Astronomical Society, 472, 104

We have converted our Titan one-dimensional photochemical model to
simulate the photochemistry of Pluto's atmosphere and include
condensation and aerosol trapping in the model. We find that
condensation and aerosol trapping are important processes in producing
the HCN altitude profile observed by the Atacama Large Millimeter Array
(ALMA). The nitrogen isotope chemistry in Pluto's atmosphere does not
appear to significantly fractionate the isotope ratio between N2 and
HCN as occurs at Titan. However, our simulations only cover a brief
period of time in a Pluto year, and thus only a brief portion of the
solar forcing conditions that Pluto's atmosphere experiences. More work
is needed to evaluate photochemical fractionation over a Pluto year.
Condensation and aerosol trapping appear to have a major impact on the
altitude profile of the isotope ratio in HCN. Since ALMA did not detect
HC15N in Pluto's atmosphere, we conclude that condensation and
aerosol trapping must be much more efficient for HC15N compared to
HC14N. The large uncertainty in photochemical fractionation makes it
difficult to use any potential current measurement of 14N/15N in
N2 to determine the origin of Pluto's nitrogen. More work is needed
to understand photochemical fractionation and to evaluate how
condensation, sublimation and aerosol trapping will fractionate N2
and HCN.

Published in:
Monthly Notices of the Royal Astronomical Society, 472, 118

We investigate the dynamics of the (47171) Lempo triple system, also
known by 1999 TC36. We derive a full 3D N-body model that takes
into account the orbital and spin evolution of all bodies, which are
assumed triaxial ellipsoids. We show that, for reasonable values of the
shapes and rotational periods, the present best fitted orbital solution
for the Lempo system is chaotic and unstable in short time-scales. The
formation mechanism of this system is unknown, but the orbits can be
stabilised when tidal dissipation is taken into account. The dynamics of
the Lempo system is very rich, but depends on many parameters that are
presently unknown. A better understanding of this systems thus requires
more observations, which also need to be fitted with a complete model
like the one presented here.

It is likely that multiple bodies with masses between those of Mars and
Earth ("planetary embryos") formed in the outer planetesimal disk of
the solar system. Some of these were likely scattered by the giant
planets into orbits with semi-major axes of hundreds of AU. Mutual
torques between these embryos may lift the perihelia of some of them
beyond the orbit of Neptune, where they are no longer perturbed by the
giant planets so their semi-major axes are frozen in place. We conduct
N-body simulations of this process, and its effect on smaller
planetesimals in the region of the giant planets and the Kuiper belt. We
find that (i) there is a significant possibility that one sub-Earth mass
embryo, or possibly more, is still present in the outer solar system;
(ii) the orbit of the surviving embryo(s) typically has perihelion of
40-70 AU, semi-major axis less than 200 AU, and inclination less than
30°; (iii) it is likely that any surviving embryos could be
detected by current or planned optical surveys or have a significant
effect on solar-system ephemerides; (iv) whether or not an embryo has
survived to the present day, their dynamical influence earlier in the
history of the solar system can explain the properties of the detached
disk (defined in this paper as containing objects with perihelia > 38 AU
and semi-major axes between 80 and 500 AU).

The centaur 95P/(2060) Chiron is showing comet-like activity since its
discovery, but the mass-loss mechanisms triggering its activity remained
unexplained. Although the collision rates in the centaur region are
expected to be very low, and impacts are thought not to be responsible
for the mass-loss, since the recent indications that Chiron might
possess a ring similar to Chariklo's, and assuming that there is debris
orbiting around, the impact triggered mass-loss mechanism should not be
excluded as a possible cause of its activity. From time series
observations collected on Calar Alto Observatory in Spain between 2014
and 2016, we found that the photometric scatter in Chiron's data is
larger than a control star's scatter, indicating a possible
microactivity, possibly caused by debris falling back to Chiron's
surface and lifting small clouds of material. We also present rotational
light curves, and measurements of Chiron's absolute magnitudes, that are
consistent with the models supporting the presumption that Chiron
possesses rings. By co-adding the images acquired in 2015, we have
detected a ∼ 5 arcsec long tail, showing a surface brightness of
25.3 mag(V)/arcsec2.

Published in:
Monthly Notices of the Royal Astronomical Society, 475, 2512

The central objective of the New Horizons prime mission was to make the
first exploration of Pluto and its system of moons. Following that, New
Horizons has been approved for its first extended mission, which has the
objectives of extensively studying the Kuiper Belt environment,
observing numerous Kuiper Belt Objects (KBOs) and Centaurs in unique
ways, and making the first close flyby of the KBO 486958 2014 MU69. This
review summarizes the objectives and plans for this approved mission
extension, and briefly looks forward to potential objectives for
subsequent extended missions by New Horizons.

The scattering trans-Neptunian Objects (TNOs) can be measured to smaller
sizes than any other distant small-body population. We use the largest
sample yet obtained, 68 discoveries by the Outer Solar System Origins
Survey (OSSOS), to constrain the slope of its luminosity distribution,
with sensitivity to much fainter absolute H magnitudes than previous
work. Using the analysis technique in Shankman et al. (2016), we
confirm that a single slope for the H-distribution is not an accurate
representation of the scattering TNOs and Centaurs, and that a break in
the distribution is required, in support of previous conclusions. A
bright-end slope of αb=0.9 transitioning to a faint-end slope
αf of 0.4-0.5 with a differential number contrast c from 1 (a
knee) to 10 (a divot) provides an acceptable match to our data. We find
that break magnitudes Hb of 7.7 and 8.3, values both previously
suggested for dynamically hot Kuiper belt populations, are equally
non-rejectable for a range of αf and c in our statistical
analysis. Our preferred divot H-distribution transitions to
αf=0.5 with a divot of contrast c=3 at Hb=8.3, while our
preferred knee H-distribution transitions to αf=0.4 at
Hb=7.7. The intrinsic population of scattering TNOs required to match
the OSSOS detections is 3×106 for Hr < 12, and 9×104
for Hr < 8.66 (D >~100 km), with Centaurs having an intrinsic
population two orders of magnitude smaller.

All surveys include observational biases, which makes it impossible to
directly compare properties of discovered trans-Neptunian Objects (TNOs)
with dynamical models. However, by carefully keeping track of survey
pointings on the sky, detection limits, tracking fractions, and rate
cuts, the biases from a survey can be modelled in Survey Simulator
software. A Survey Simulator takes an intrinsic orbital model (from, for
example, the output of a dynamical Kuiper belt emplacement simulation)
and applies the survey biases, so that the biased simulated objects can
be directly compared with real discoveries. This methodology has been
used with great success in the Outer Solar System Origins Survey (OSSOS)
and its predecessor surveys. In this chapter, we give four examples of
ways to use the OSSOS Survey Simulator to gain knowledge about the true
structure of the Kuiper Belt. We demonstrate how to statistically
compare different dynamical model outputs with real TNO discoveries, how
to quantify detection biases within a TNO population, how to measure
intrinsic population sizes, and how to use upper limits from
non-detections. We hope this will provide a framework for dynamical
modellers to statistically test the validity of their models.

The dates for the international science conference on the Pluto system
and the Kuiper Belt have been moved to 2019 July 12-16 (Friday-Tuesday).
Please mark your calendars accordingly!
Unfortunately, these new dates span a weekend, but that was unavoidable
owing to conflicts with two other major conferences (a lunar conference
coinciding with the 50th anniversary of Apollo 11 and the Ninth
International Conference on Mars). The venue remains the same: The Johns
Hopkins University Applied Physics Laboratory in Laurel, MD, USA.

There will be a reception commemorating the 4th anniversary of the Pluto
flyby during the evening of July 14th.

This conference will provide an opportunity to summarize our
understanding of the Pluto system and the Kuiper belt following the New
Horizons encounters with Pluto and 2014 MU69.
Contributions spanning all relevant research on the Kuiper belt,
including both observations and theory, will be solicited.
The conference will also serve as a nucleus for a forthcoming volume
"Pluto After New Horizons" in the University of Arizona Space Science
Series. With a projected 2020 publication date, this new book will be
the successor to "Pluto-Charon" published in 1997.

A registration website with further details will be set up this summer,
approximately one year prior to the conference.
Again, please put this conference on your calendar and join us at the
Kossiakoff Center at APL in mid-July 2019!

São Paulo State University - UNESP in Guaratinguetá
National Institute for Space Research - INPE in São José dos Campos

The Group of Orbital Dynamics and Planetology invites applications for post-doc positions. There are 5 positions that will be funded by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo). The candidates must have experience on Planetary Dynamics and/or Spacecraft Dynamics. The projects to be developed are the following:

Attitude and orbit analysis for a mission to a triple asteroid system;

Spin-orbit coupling in Solar System dynamics;

Dynamics involving small bodies under gravitational close approaches;

Planetary Formation.

The projects will be developed in one of the following institutions:

São Paulo State University - UNESP in Guaratinguetá

National Institute for Space Research - INPE in São José dos Campos

Applicants should send a statement of research interest and a curriculum vitae
with a list of publications to: Prof. Silvia Giuliatti Winter ( giuliattiwinter@gmail.com ).

Deadline of applications: March, 3, 2018

. .

PhD Scholarships

São Paulo State University - UNESP
National Institute for Space Research - INPE in São José dos Campos-Brazil

The Group of Orbital Dynamics & Planetology invites applications for PhD scholarships
that will be funded by FAPESP (Fundação de Amparo à Pesquisa do Estado de
São Paulo). The PhD Program and the scholarships have duration of four years.
The candidates should not have obtained the Master Degree. The projects to be developed
are in the following topics:

Origin, formation and evolution of satellites and planetary rings;

Deflection of an asteroid in a collision route to the Earth.

The projects will be developed in the São Paulo State University - UNESP
or in the National Institute for Space Research - INPE in São José dos Campos-Brazil.

Applicants should send a statement of research interest and a
curriculum vitae to Prof. Giuliatti Winter ( giuliattiwinter@gmail.com ).

Deadline of applications: April, 13, 2018

Newsletter Information

The Distant EKOs Newsletter is dedicated to provide researchers with
easy and rapid access to current work regarding the Kuiper belt (observational
and theoretical studies), directly related objects (e.g., Pluto, Centaurs), and
other areas of study when explicitly applied to the Kuiper belt.

We accept submissions for the following sections:

Abstracts of papers submitted, in press, or recently published in refereed journals

Titles of conference presentations

Thesis abstracts

Short articles, announcements, or editorials

Status reports of on-going programs

Requests for collaboration or observing coordination

Table of contents/outlines of books

Announcements for conferences

Job advertisements

General news items deemed of interest to the Kuiper belt community

A LaTeX
template for submissions is appended to each issue of the newsletter, and
is sent out regularly to the e-mail distribution list. Please use that
template, and send your submission to:

Recent and back
issues of the Newsletter are archived there in various formats. The web
pages also contain other related information and links.

Distant EKOs is not a refereed publication, but is a tool for
furthering communication among people interested in Kuiper belt research.
Publication or listing of an article in the Newsletter or the web page does
not constitute an endorsement of the article's results or imply validity of its
contents. When referencing an article, please reference the original source;
Distant EKOs is not a substitute for peer-reviewed journals.

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